Download Tutorial 1 - University of Prince Edward Island

Pathology of the Cardiovascular System
Alfonso López
Professor of Anatomic Pathology
Dept. Pathology and Microbiology
Atlantic Veterinary College
University of Prince Edward Island
Canada
Jan 23, 2013
Module 1 Structure and Function
Heart: Structure and Function
• The heart is the first organ to form in the embryo. • In mammalians and birds it consists of 4 chambers (2 atria and 2 ventricles). • There are four cardiac valves:
1.
2.
3.
4.
Right atrio‐ventricular (Tricuspid)
Left atrio‐ventricular (Mitral)
Aortic (semilunar)
Pulmonic Source: Wikipedia
In the adult animal the left ventricle is thicker than the right
Heart: Structure and Function
• The systemic circulation returns non‐
oxygenated blood from the body to the right atrium via the vena cava.
• From the right atrium the blood passes through the right AV valve into the right ventricle.
• From the right ventricle the blood is pumped into the lungs via the pulmonary (pulmonic) arteries.
• From the lung, oxygenated blood returns to the left atrium via the pulmonary vein.
• The blood then passes from the left atrium to the left ventricle through the mitral valve. Source: Wikipedia
Heart: Structure and Function
The heart is composed of three layers: 1. Pericardium (Epicardium).
2. Myocardium (Heart muscle).
3. Endocardium (atria, ventricles and valves).
2‐ Myocardium
3‐ Endocardium
1‐ Epicardium
Pericardium and Epicardium
Pericardium and Epicardium:
*
•
The pericardium is a double layered serosal membrane that covers the heart and the proximal part of the great vessels.
•
The most external and thicker layer of the sac is the parietal pericardium while the most internal and thinner layer which intimately covers the myocardium, is the visceral pericardium called epicardium.
•
These two serosal membranes are composed of a thin layer of mesothelium and connective tissue which supports blood vessels, lymphatic vessels, nerves and adipose tissue. •
The epicardial fat (asterisk) generally follows the coronary grooves. •
The pericardial space ,present between the epicardium and pericardium, contains small amounts of clear lubricant fluid.
Note: The pericardial sac (pericardium) was removed to expose the epicardium
Epicardial surface
Epicardial fat
Epicardium
Nerve
Myocardium
Artery
Myocardium
Myocardium
• The myocardium constitutes the muscle of the heart.
• Through contraction (systole) and relaxation (diastole) the heart pumps the blood to the lungs and systemic circulation. • The myocardial muscle is histologically similar but not identical to skeletal muscle.
Myocardium
•
Involuntary striated muscle.
•
Branched fibres that connect with each
other through the Intercalated disks (white
arrows).
•
Fibres contain abundant mitochondria but
these sre only seen by electron
microscopy.
Endocardium
•
Thin layer lining the internal
surface of the heart.
•
Endocardium in the heart is the
equivalent to the tunica intima of
blood vessels.
•
It is close contact with blood.
•
Endocardium is microscopically
composed of three layers:
1. Endothelium (superficial)
2. Basal lamina
3. Sub-endothelial connective
tissue (elastin and collagen).
•
Endocardium also contains part
of the conductive system and
Purkinje fibres.
Endocardium
Purkinje Fibers
•
Specialized myocardial cells (arrow)
•
Responsible for electrical impulse conduction
•
Not to be confused with Purkinje cells in the cerebellum
Endocardium
Myocardium
Normal Heart Valves
The heart has four valves which allow for unidirectional blood flow: 1. Tricuspid valve (right AV valve)
2. Bicuspid or mitral valve (left AV valve)
3. Aortic (semi‐lunar) valve
4. Pulmonic valve (pulmonary artery.
The normal valvular leaflets (cusps) are thin, smooth, partially translucent and are lined by endothelium.
Normal Heart Valves
Atrium
Endocardium
Valve
Chordae tendinae
AV valves attach to the papillary muscles of the ventricular myocardium by the chordae tendinae.
Papillary muscle
Postmortem Examination of the Heart
Silhouette in situ
Shape
Size
Weight (total and ratios)
Color
Pericardial fluid
Fat deposits
Post‐mortem changes
Wall thickness
Valves
Endocardium
Blood vessels
Postmortem Examination
Equine Thorax
•
Always check the heart in situ paying attention to the relative size of the cardiac silhouette (dotted lines).
•
Before cutting the pericardium (arrow), check for the presence of effusions or exudate.
Enlarged cardiac silhouette occurs in: cardiac dilation or hypertrophy, pericarditis, tumor or cardiac effusions.
Note an enlarged cardiac silhouette with marked cardiac dilation which in this lamb is secondary to heart defect.
Note severe hydropericardium which is secondary to a right heart failure
Postmortem Examination of the Heart
There is no universal method to open a heart. In neonatal and young animals it is important to carefully check for congenital heart defects.
Postmortem Examination
Before you open the heart, check the epicardium, pericardial fat and great vessels Left Atrium
The atrial epicardium is slightly thicker which gives it a whiter appearance
Epicardial fat
It follows the coronary groove
Epicardium
Thin and transparent serosal
membrane through which the underlying myocardium is visible.
Opening the Right Heart
Pulmonic artery
Right ventricle
The most frequent technique to examine the heart, is to cut the right ventricle in a “U” shape starting in the pulmonary artery and ending to the base of the right atrium (yellow lines). Opening the Left Heart
The left ventricle is opened with a single straight cut extending from the apex to the left atrium (yellow lines) The Left Heart
Finally, open the aortic outflow tract by inserting a knife or cutting through the mitral valve with scissors (white arrow). Once the aortic outflow is visible carefully check the semilunar valves (black arrows).
LV
Septum
RV
Some pathologists like to make a transverse section of the heart to evaluate the wall thickness of the ventricles and septum (arrows). Typically the left ventricle (LV) is 2‐3 times thicker than the right ventricle (RV).
Caution: Do not mistake lymphatic vessels in the epicardium (arrows) with heart lesions. This mistake is particularly common when examining the hearts of emaciated animals. Samples for Histopathology
Take representative samples of atrium, ventricles, and septum in a routine post‐mortem, and valves if you suspect valvular problems. For better fixation, wash away excess blood before putting tissues in the formalin and use a tissue:fixative volume ratio of 1:10.
 Thanks to all AVC pathologists for contributing case materials
 Some images were acquired from veterinary colleges of
Canada, United States and Mexico and the names of some
contributing pathologists are unknown. Their valuable
contribution is sincerely acknowledged.
 I would like to thank Dr. Shannon Martinson, Atlantic
Veterinary College, for critically reviewing these modules.
Module 1: Structure and Function
THE END
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